This invention relates to a multilayer wiring substrate. An example of prior art multilayer wiring substrates with engineering change pads is disclosed in a paper entitled "Thermal Conduction Module: A High-Performance Multilayer Ceramic Package" by A. J. Blodgett et al., published in the IBM Journal of Research and Developments, Vol. 26, No. 1, January 1982, pp 30 to 36, and U.S. Pat. No. 4,245,273. In the U.S. Pat. No. 4,245,273, each of engineering change pads 20 comprises a pad portion 24 for connecting a wire 38 at the time of the engineering change and a link portion 26 to be severed when attempting such an engineering change. Both the portions 24 and 26 are identical in terms of their layer structures and materials.
In the prior art substrate, when the wire 38 is solderbonded to the pad portion 24 it is necessary, to form a solder dam on the pad 20 to prevent solder from flowing out over wiring patterns exposed on the substrate. Since the process of forming the solder dam requires the steps of pattern forming and firing, the whole pad 20 should be fabricated with a metal or metals which do not produce oxides. The prior art substrate, therefore, has the disadvantage in that pads cannot be fabricated exclusively with the materials satisfactory in solder wettability and severability.
An object of the invention is, therefore, to provide a substrate free from the above-mentioned disadvantage of the prior art substrate.